Preparation of alkyl glycosides

ABSTRACT

Alkyl glycosides are prepared by reacting alcohols with monosaccharides or compounds which, under the reaction conditions, form monosaccharides, in the presence of amphoteric surfactants in the acid form as catalysts, and subsequently neutralizing the reaction mixture with bases.

The present invention relates to a process for preparing alkylglycosides by reacting alcohols with monosaccharides or compounds which,under the reaction conditions, form monosaccharides, in the presence ofacid catalysts, and subsequently neutralizing the reaction mixture withbases.

Surface-active alkyl glycosides, which are mainly used for detergentsand cleaners, have been known for a long time. They are prepared on theindustrial scale by two different processes, either by direct synthesisin which the long-chain alcohol component is directly linked to thesugar component with elimination of water, or by the transacetalizationmethod in which a short-chain alkyl glycoside is initially prepared andthen, in a second stage, reacted with long-chain alcohols to give thesurface-active alkyl glycoside. Acid catalysts are required for bothprocesses. Thus, for example, U.S. Pat. No. 3 598 865 discloses the useof sulfuric acid, hydrochloric acid, phosphoric acid, phosphorous acid,toluenesulfonic acid or boron trifluoride as catalyst. As is evidentfrom U.S. Pat. No. 3 839 318, direct reaction of saccharides andlong-chain alcohols can also be carried out in the presence of acid ionexchangers. EP-B-132 043 discloses the use of anionic surfactants in theacid form as catalyst for preparing alkyl glycosides. DE-A-3 927 919discloses the use of sulfosuccinic acid as catalyst in the preparationof alkyl glycosides. WO-A-90/07 516 discloses the use ofdialkylnaphthalenesulfonic acids as catalyst in the preparation of alkylglycosides. The abovementioned catalysts have various disadvantages. Inparticular, sulfuric acid and phosphoric acid lead to the formation ofpolysaccharides during the reaction of the alcohols withmonosaccharides. In addition, the products obtained on use of thesecatalysts are highly colored. Other catalysts, such as anionicsurfactants in the acid form, eg. dodecylbenzenesulfonic acid, likewiseyield alkyl glycosides with relatively high color numbers.

It is an object of the present invention to provide a process forpreparing alkyl glycosides in which the formation of polyglycosides fromthe monosaccharides is greatly reduced and in which the reactionproducts have a very low iodine number.

We have found that this object is achieved by a process for preparingalkyl glycosides by reacting alcohols with monosaccharides or compoundswhich, under the reaction conditions, form monosaccharides, in thepresence of acid catalysts, and subsequently neutralizing the reactionmixture with bases, wherein amphoteric surfactants in the acid form areemployed as catalysts. Amphoteric surfactants which are particularlypreferably used are quaternary eminoalkylsulfonates, quaternaryaminoalkyl sulfates or mixtures thereof.

In the literature, the emphoteric surfactants are also called sulfobetaines or sulfato betaines. They can also be employed in the form ofthe alkali metal or ammonium salts as catalyst. However, in this case itis necessary to liberate the free acid therefrom by adding a strongacid, eg. sulfuric acid or hydrochloric acid. The liberation of the acidcan be carried out separately from the preparation of the alkylglycosides or else take place in the reaction medium itself.

The amphoteric surfactants in the acid form are suitable for preparingall alkyl glycosides disclosed to date. The alkyl glycosides may bedescribed by the formula RO(G)_(m) where

G is a saccharide unit,

m is from 1 to 12, preferably 1 to 4, and

R is an aliphatic radical with 1 to 30 carbons.

The saccharide unit G may comprise the customary aldoses and ketoses,eg. glucose, fructose, mannose, galactose, talose, gulose, allose,altrose, idose, arabinose, xylose, lyxose and ribose. Also possible aresaccharide mixtures, oligosaccharides, eg. maltose, lactose andpalatinose, or mixtures of mono- and oligosaccharides. The saccharidescan be employed both in anhydrous form and with water of crystallizationor else as aqueous syrup. The use of an aqueous saccharide syrup ispreferred for economic reasons. The water content of the aqueoussaccharide syrup is from 10 to 80, preferably from 15 to 60, % byweight. Industrial solutions with water contents of 20-40% by weight arepreferably used. The saccharide preferably used is an aqueous glucosesyrup or glucose.

Compounds which form monosaccharides under the reaction conditions areoligo- and polysaccharides. C₁ -C₅ -alkyl glycosides which aretransacetalized with C₆ -C₃₀ alcohols can also be regarded as compoundswhich form monosaccharides under the reaction conditions.

The alcohols used to form the alkylglycosides can have any desired chainlength from C₁ to C₃₀. Primary aliphatic alcohols are preferablyemployed. To prepare surface-active glycosides which are employed assurfactant raw materials in detergents and cleaners, preferably primaryaliphatic alcohols with from 6 to 20, in particular with from 8 to 16,carbons are reacted with monosaccharides or compounds which formmonosaccharides under the reaction conditions. The higher aliphaticalcohols are prepared, for example, from industrial fats. However, itis, of course, also possible to employ synthetic primary alcohols, eg.oxo alcohols, as reaction component. Diols can also be employed asalcohol component, eg. ethylene glycol, proylene glycols, butanediolssuch as 1,4-butanediol and hexanediols, especially 1,6-hexanediol. Diolswhich can also be used are 1,2- and 1,3-alkanediols with the structures##STR1## Hydroxyalkyl glycosides are obtained when diols are used.

The higher aliphatic primary C₈ -C₁₈ alcohols which are preferred arepreferably saturated and, in particular, straight-chain alcohols whichare prepared by hydrogenation of natural fatty acids on the industrialscale. Typical examples of the higher aliphatic alcohols are n-dodecylalcohol, n-tetradecyl alcohol, n-hexadecyl alcohol, n-octadecyl alcohol,n-octyl alcohol, decyl alcohol, undecyl alcohol and tridecyl alcohol.Since the fatty alcohols are preferably prepared from natural fats; theynormally take the form of technical mixtures, which are also employed toprepare the alkyl glycosides. Apart from the fatty alcohols obtainedfrom natural fats, also suitable for the reaction are branched primaryalcohols, for example oxo alcohols. Typical examples of oxo alcohols areC₁₂ /C₁₃ alkanols with about 25% methyl branching, mainly in position 2(Dobanol 23), and the corresponding C₉ -C₁₁ alcohols (Dobanol 91).However, the alcohols obtainable from natural fats are preferably used.

The reaction of the alcohols with the monosaccharides or compounds whichform monosaccharides under the reaction conditions takes place accordingto the invention in the presence of amphoteric surfactants in the acidform. Alkyl glycosides of the formula RO(G)_(m) where G and R have theabovementioned meanings, and m is from 1 to 12, are obtained. The valueof m should be as small as possible because the alkyl polyglycosideswhich are produced in minor amounts in the reaction have less detergentpower than the alkyl monoglycosides. The value of m is thereforepreferably from 1.1 to 1.5. The alkyl glycosides produced in thereaction are mixtures of alkyl mono- and oligoglycosides. It istherefore also possible for m not to be a whole number. Besides thealkyl glycosides, it is also possible for unwanted polysaccharides ofvarious composition to be formed by polymerization of the saccharides.However, this reaction is substantially suppressed when the amphotericsurfactants in the acid form are used according to the invention.

Examples of amphoteric surfactants in the acid form are: ##STR2##

Quaternary aminoalkylsulfonates and quaternary aminoalkyl sulfates inthe acid form can be described, for example, by the following formulae:##STR3## In the formulae I to IV, R is C₈ -C₃₀ -alkyl, R¹ is C₁ -C₂₀-alkyl and X is an anion, preferably HSO₄ -, SO₄ ²⁻ and Cl⁻. The valueof n is 0-10 in formula I and 2-10 in each of formulae III and IV. Thevalue of m in formula IV is 1-6.

Examples of compounds of the formula I are dimethyl(3-sulfopropyl)stearylammonium chloride and dimethyl(3-sulfopropyl)laurylammonium chloride.

Examples of suitable compounds of the formula II are dimethyl(2-hydroxy-3-sulfopropyl)laurylammonium chloride anddimethyl(2-hydroxy-3-sulfopropyl)stearylammonium chloride.

Examples of suitable compounds of the formula III aredimethyl(3-hydroxysulfonyloxypropyl)laurylammonium chloride anddimethyl(3-hydroxysulfonyloxypropyl)stearylammonium chloride.

An example of compounds of the formula IV is dimethyl(3-sulfopropyl)-3-stearylcarbamoylpropylammonium chloride.

The compounds of the formulae I to IV indicated above can be employednot only in the acid form but also in the form of the sulfonic acidsalts as catalyst in the preparation of alkyl glycosides. However, it isthen necessary for the amphoteric surfactants to be in the acid formproduced by addition of strong acids such as sulfuric acid orhydrochloric acid to their salts. The liberation of the free acids ofthe amphoteric surfactants from the salts can also take place in thereaction medium.

The process according to the invention is preferably used to preparealkyl glycosides from alcohols with from 6 to 30 carbons. Based on themonosaccharides employed in the reaction, the amphoteric surfactants inthe acid form are used in amounts of from 0.1 to 5, preferably 0.1 to0.5, mol %. The amounts of amphoteric surfactants in the acid formnormally employed as catalysts are less than the amounts of catalystsotherwise used. The direct reaction of glucose syrups with long-chainalcohols can be carried out without the emulsifiers which are normallyadded. The alkyl glycosides which are prepared using amphotericsurfactants in the acid form have a paler color than alkyl glycosidesprepared with other catalysts. In addition, less bleach is needed tobleach the glycosides obtained by the process according to the inventionthan for alkyl glycosides obtained by known processes.

The percentages in the examples are by weight.

The following catalysts were used in the examples:

Catalyst 1: Dimethyl(3-sulfopropyl)laurylammonium betaine (RALUFON DL),protonated with sulfuric acid

Catalyst 2: Coconut fatty dimethyl(3-sulfopropyl)ammonium betaine(RALUFON DCH), protonated with sulfuric acid

Catalyst 3: Dimethyl(3-sulfopropyl)stearylammonium betaine (RALUFON DS),protonated with sulfuric acid.

The following catalysts were tested for comparison with the prior art:

Catalyst 4: Dodecylbenzenesulfonic acid

Catalyst 5: p-Toluenesulfonic acid

Catalyst 6: Sulfuric acid.

EXAMPLE 1A)

1033 g of a C₈ -C₁₀ fatty alcohol mixture (Lorol 810 S) were introducedinto a 2 l multi-neck flask equipped with stirrer, baffles, thermometer,distillation head and a metering unit comprising a metering pump, apressure-maintaining valve and a nozzle, and 3 g of dimethyl(3-sulfopropyl)laurylammonium betains (Ralufon DL) and 0.46 g of 96%strength sulfuric acid were added. The amount of amphoteric surfactantin the form of the sodium salt was 0.5 mol % based on glucose. Thismixture was mixed with 21 g of a C₈ /C₁₀ -alkyl glucoside/C₈ -C₁₀ fattyalcohol mixture as emulsifier. The emulsifier mixture contained about65% alcohols and about 35% glucose. The solution was heated to 115°-120°C., and the pressure was adjusted to from 50 to 60 mbar. Then 485 g of aglucose syrup (65% strength aqueous solution) preheated to 60° C. wereadded continuously. At the same time, the water introduced with theglucose syrup into the system was removed by distillation. After ametering time of 4 hours, the reaction mixture was then maintained atabout 120° C. for 30 minutes. The result was a slightly cloudy, paleyellow reaction solution which was cooled and then neutralized with 50%strength aqueous sodium hydroxide solution. The excess alcohol was thenremoved by distillation, and the residue was converted into a 60%strength aqueous solution, which was bleached with 6 g of 30% strengthhydrogen peroxide solution at 80° C. The iodine color number of thebleached reaction solution was 5.

EXAMPLES 1b) AND 1c), AND COMPARATIVE EXAMPLES 1-3

Example 1a) was repeated with the catalysts shown in Table 1. Theresults obtained with these are indicated in Table 1, specifically theamount of polyglucose in the reaction mixture, the hydrogen peroxideused to bleach the reaction mixture, and the color number of thebleached reaction mixture.

                  TABLE 1                                                         ______________________________________                                                                           Iodine                                                       Polyglucose      color No. of                                                 [%] in the H.sub.2 O.sub.2                                                                     the bleached                                        Catalyst reaction   used  reaction                                   Example 1                                                                              No.      mixture    [g]   mixture                                    ______________________________________                                        a)       1        6          6.0   5                                          b)       2        8          6.0   7.5                                        c)       3        4          4.5   4                                          Comparative                                                                   Examples                                                                      1        4        4          6.0   10                                         2        5        18         9.0   18.5                                       3        6        25         12.0  25                                         ______________________________________                                    

EXAMPLE 2

a) Example 1a) was repeated with catalyst 3.

b) Example 1a) was repeated but with omission of the emulsifier and useof catalyst 3 in place of catalyst 1. The results are indicated in Table2.

COMPARATIVE EXAMPLE 4

Example 1a) was repeated but with catalyst 4 in place of the catalystused there.

COMPARATIVE EXAMPLE 5

Example 1a) was repeated but with omission of the emulsifier describedin Example la) and using the catalyst 4 in place of the catalystdescribed there. The results are indicated in Table 2.

                  TABLE 2                                                         ______________________________________                                                                           Iodine                                                       Polyglucose      color No. of                                                 [%] in the H.sub.2 O.sub.2                                                                     the bleached                                        Catalyst reaction   used  reaction                                   Example 1                                                                              No.      mixture    [g]   mixture                                    ______________________________________                                        a        3        4          4.5   4                                          b        6        6.0        8                                                Comparative                                                                   Examples                                                                      4        5        9          6.0   10                                         5        4        **         10.0  12                                         ______________________________________                                         ** Heavy precipitate after the metering phase, composed of about 80-90%       polyglucose                                                              

EXAMPLE 3

a) Example 1a) was repeated with catalyst 3. The catalyst concentrationwas 0.5 mol % based on glucose. The results are indicated in Table 3.

b) Example 1a) was repeated by using, in place of the catalyst employedthere, catalyst 3 in an amount of 0.1 mol % based on glucose. Theresults are indicated in Table 3.

COMPARATIVE EXAMPLE 6

Example 1 was repeated but employing catalyst 4 in a concentration of0.1 mol % based on glucose. The results are indicated in Table 3.

                  TABLE 3                                                         ______________________________________                                                           Cat. conc.                                                                              Polyglucose                                                                            Residue                                                    [mol %    [%] in the                                                                             after                                   Example  Catalyst  based on  reaction metering                                3        No.       glucose]  mixture  phase                                   ______________________________________                                        a        13        0.5       4        none                                    b        13        0.1       4        none                                    Comparative                                                                            4         0.1       12       29 g                                    Example                                                                       ______________________________________                                    

We claim:
 1. A process for preparing alkyl glycosides by reactingalcohols with monosaccharides or compounds which, under the reactionconditions, form monosaccharides, in the presence of acid catalysts, andsubsequently neutralizing the reaction mixture with bases, whereinamphoteric surfactants in the acid form are employed as catalysts.
 2. Aprocess as claimed in claim 1, wherein quaternary aminoalkylsulfonates,quaternary aminoalkyl sulfates or mixtures thereof are employed asamphoteric surfactant.
 3. A process as claimed in claim 1 or 2, whereinalcohols with from 8 to 30 carbons are employed.
 4. A process as claimedin claim 1 or 2, wherein the amphoteric surfactants are employed inamounts of from 0.1 to 5 mol % based on monosaccharides.